Amplified Detection of Iron Ion Based on Plasmon Enhanced Fluorescence and Subsequently Fluorescence Quenching

A facile and rapid approach for detecting low concentration of iron ion(Fe3+) with improved sensitivity was developed on the basis of plasmon enhanced fluorescence and subsequently amplified fluorescence quenching.Au1Ag4@Si O2 nanoparticles were synthesized and dispersed into fluorescein isothiocyanate(FITC) solution. The fluorescence of the FITC solution was improved due to plasmon enhanced fluorescence. However, efficient fluorescence quenching of the FITC/Au1Ag4@Si O2 solution was subsequently achieved when Fe3+, with a concentration ranging from17 n M to 3.4 l M, was added into the FITC/Au1Ag4@Si O2 solution, whereas almost no fluorescence quenching was observed for pure FITC solution under the same condition. FITC/Au1Ag4@Si O2 solution shows a better sensitivity for detecting low concentration of Fe3+compared to pure FITC solution. The quantized limit of detection toward Fe3+was improved from 4.6 l M for pure FITC solution to 20 n M for FITC/Au1Ag4@Si O2 solution.

Gap-plasmon of Fe3O4@Ag Core-shell Nanostructures for Highly Enhanced Fluorescence Detection of Rhodamine B

A novel gap-plasmon of Fe3O4@Ag core-shell nanoparticles for surface enhanced fluorescence detection of Rhodamine B（RB） was developed. Fe3O4@Ag core-shell nanostructures with Ag shell and Fe3O4 core were synthetized by self-assembled method with the assistance of 3-mercaptopropyl trimethoxy silane（MPTS）. To study the RB fluorescence enhanced by gap-plasmon, the fluorescence properties of RB on the substrates with different nanogap densities were systematically investigated, and the results showed that the fluorescence intensity of RB on Fe3O4@Ag core-shell NPs substrate was much stronger than that on bare glass substrate, and the fluorescence intensity was further improved by using multilayer Fe3O4@Ag core-shell NPs substrate which had higher nanogap density. Different from the mechanism that is based on the maximum overlap of the surface plasmon resonance（SPR） band and emission band, the mechanism of the fluorescence enhancement in our work is based on the localized surface plasmon（LSP） and the gap plasmon near-field coupling with the Fe3O4@Ag core-shell NPs. Besides, the detection limit obtained was as low as 1×10^（-7） mol/L, and the Fe3O4@Ag core-shell NPs substrate had high selectivity for RB fluorophores. It was demonstrated that the Fe3O4@Ag core-shell NPs substrate had activity, good stability, and selectivity for fluorescence detection of RB. And the detection of RB by the surface plasmon enhanced fluorescence was more convenient and rapid than the traditional detection methods in previous works.

Enhanced fluorescence sensing of tetracycline with Ti_(2)C quantum dots

Ti_(2)C quantum dots(QDs)with rich surface functional groups have been synthesized using a hydrothermal method,and used to detect tetracycline(Tc)based on enhanced fluorescence.The interaction between the surface functional groups of Ti_(2)C QDs and Tc enhanced the fluorescence of Tc at 514 nm,which is used to detect Tc quickly and accurately.Under optimal conditions,the fluorescence intensity was linear to the concentration of Tc in the range of 50.0–30.0μM,with a detection limit of 21.6 nM.Furthermore,the Tc-Ti_(2)C QDs detection system was evaluated for detection of Tc in milk and artificial urine.This study demonstrates a new and simple strategy for Tc detection,which is important for food safety and human health.

Ultrasensitive and accurate diagnosis of urothelial cancer by plasmonic AuNRs-enhanced fluorescence of near-infrared Ag_(2)S quantum dots

Urothelial carcinoma(UC)is a common malignant tumor in the urinary system with high recurrence rate and low survival rate 5 years after surgery.At present,imaging examination and other diagnostic methods have some shortcomings such as invasiveness and non-specificity.Therefore,it is urgent to develop a simple,rapid,noninvasive,highly sensitive and highly specific strategy to diagnose UC.Herein,a high-performance fluorescence sensor was constructed by the plasmonic gold nanorods(AuNRs)-enhanced near-infrared(NIR)fluorescence of silver sulfide quantum dots(Ag_(2)S QDs).The designed sensor can be used for the fast and accurate detection of small molecule single-transmembrane protein(FXYD3),which is overexpressed in 90%of ureteral cancers and 84%of high-grade bladder cancers.Due to its high specificity,the NIR fluorescence sensor achieves the detection of FXYD3 in the range of 0.25-150 ng·ml^(-1)with a detection limit of 0.2 ng·ml^(-1).Importantly,it also can be used for accurate diagnosis of FXYD3 in the urine of patients with relevant cancers,and the results are consistent with clinical cystoscopy and pathological analysis.The proposed fluorescence sensor provides a simple,ultrasensitive,reliable method for UC screening,tumor-grade classification and postoperative monitoring and will have great potential for clinical applications.

Thermal-annealing-regulated plasmonic enhanced fluorescence platform enables accurate detection of antigen/antibody against infectious diseases

Plasmonic enhanced fluorescence(PEF)technology is a powerful strategy to improve the sensitivity of immunofluorescence microarrays(IFMA),however,current approaches to constructing PEF platforms are either expensive/time-consuming or reliant on specialized instruments.Here,we develop a completely alternative approach relying on a two-step protocol that includes the self-assembly of gold nanoparticles(GNPs)at the water–oil interface and subsequent annealing-assisted regulation of gold nanogap.Our optimized thermal-annealing GNPs(TA-GNP)platform generates adequate hot spots,and thus produces high-density electromagnetic coupling,eventually enabling 240-fold fluorescence enhancement of probed dyes in the near-infrared region.For clinical detection of human samples,TA-GNP provides super-high sensitivity and low detection limits for both hepatitis B surface antigen and SARS-CoV-2 binding antibody,coupled with a much-improved detection dynamic range up to six orders of magnitude.With fast detection,high sensitivity,and low detection limit,TA-GNP could not only substantially improve the outcomes of IFMA-based precision medicine but also find applications in fields of proteomic research and clinical pathology.

Nanoscaled ZnO films used as enhanced substrates for fluorescence detection of dyes

The ability of nanoscaled ZnO films to enhance fluorescence was studied. We found that the fluorescence intensities of Cy5, rhodamine 6G, and fiuorescein can be enhanced about 10-fold on nanoscaled ZnO films as compared to that on glass substrates. The lifetimes of all samples were measured, and no obvious change in lifetime was observed for dyes on different substrates. The mechanism for the nanoscaled ZnO film enhanced fluorescence appears to be different from that for the metal-fluorophore systems.

Highly oxidized graphene with enhanced fluorescence and its direct fluorescence visualization

We prepared hyper-oxidized graphene(HOG) as a form of graphene derivative by additional oxidation of graphene oxide(GO) sheets. HOG, which formed more functional groups and isolated conjugated clusters on the sheets, accordingly showed high solubility in water and alcohols, high transmittance and film transparence, longer fluorescence decay constant time, and enhanced fluorescence in states of solution and solid. By contrast, GO has much weaker fluorescence in solution and its fluorescence is totally quenched in solid. The influences of concentration, metallic ions, and pH on HOG fluorescence in aqueous solution were also investigated in detail. Due to HOG's strong fluorescence, direct visualization was realized on substrates and in solution. In addition, direct 3D fluorescence visualizations of HOG phase in polymer composites were achieved. These results show the great potential of HOG in a broad range of applications, from biological labeling, probes, and drug carriers to highperformance composites and nanomanipulation.

Ultrasonic-Assisted Synthesis of Monodisperse Ag Nanoparticles and Their Applications in Surface Enhanced Raman Scattering and Fluorescence Enhancement

Monodisperse Ag nanoparticles with diameters of about 3.4 nm were synthesized by a facile ultrasonic synthetic route at room temperature with the reduction of borane-tert-butylamine in the presence of oleylamine （OAm） and oleic acid （OA）. The reaction parameters of time, the molar ratios of OAm to OA were studied, and it was found that these parameters played important roles in the morphology and size of the products. Meanwhile, surface enhanced Raman spectrum （SERS） property suggested the Ag nanoparticles exhibited high SERS effect on the model molecule Rhodamine 6G. And also, two-photon fluorescence images showed that the silver nanoparticles had high performances in fluorescence enhancement.

Ag Nanowire-Ag Nanoparticle Hybrids for the Highly Enhanced Fluorescene Detection of Protoporphyrin IX Based on Surface Plasmon-Enhanced Fluorescence

In this study, we developed an approach to fabricate novel 1D Ag NWs-Ag NPs hybrid substrate for enhanced fluorescene detection of protoporphyrin 1X （PplX） based on surface plasmon-enhanced fluorescence. The Ag NWs-Ag NPs hybrid was synthesized by combining the hydrothermal method and self-assembly method with the asisstance of polyvinylpyrrolidone （PVP）. When the Ag NWs-Ag NPs hybrid was deposited on the glass substrate and employed as active substrate to detect PplX, the fluorescence intensity of PplX was enhanced greatly due to the coupling effect of localized surface plasmon-localized surface plasmon （LSP-LSP） and localized surface plasmon- surface plasmon propagation （LSP-SPP） which induced great enhancement of the electromagnetic field. Furthermore, the enhancement effect was approximately linear when the concentration of PpIX was ranged from 1×10^-7 mol/L to 2×10^-5 mol/L, and the photobleaching phenomenon of PplX was reduced greatly, indicating that the fab- ricated Ag NWs-Ag NPs hybrid substrate had well performance for PplX imaging. This work provides an effective approach to prepare highly sensitive and stable fluorescence enhancement substrate, and has great potential application in fluorescence imaging.

Large-scale controllable fabrication of aluminum nanobowls for surface plasmon-enhanced fluorescence

Al nanoparticles(NPs)exhibit excellent localized surface plasmon resonance(LSPR)properties and have been considered a promising alternative to plasmonic Au or Ag NPs.However,it remains difficult to fabricate Al NPs with uniform size and controllable morphology over a large area on substrates,which seriously hinders the in-depth exploration of their properties and applications.Herein,we have developed a self-assembly nanoparticle template method to realize the controllable preparation of bowl-shaped Al NPs(Al nanobowls(Al NBs))with tunable sizes from 36 to 131 nm on the substrate surface,accompanied by tunable LSPR spectral responses from 272 to 480 nm.Among them,131 nm Al NBs exhibit superior fluorescence enhancement ability(1932.2-fold)and a low detection limit(78.6 pM)towards 5-carboxyfluorescein,exceeding comparable Ag NBs and Au nanospheres(NSs).This can be attributed to the strong electromagnetic enhancement induced by the LSPR effect and the effective inhibition of fluorescence quenching caused by the self-passivated oxide layer.Therefore,the successful fabrication of Al NBs on substrates is of vital significance for their promising applications,including surface-enhanced spectroscopy,sensitive fluorescence detection,light-harvesting devices,biosensing,and ultraviolet(UV)plasmonics.

Au NP@silica@europium coordination polymer nanocomposites for enhanced fluorescence and more sensitive monitoring reactive oxygen species

Au nanoparticle（Au NP）@SiO2@TDA-Eu nanocomposites were prepared by a two-step process： Au NP@SiO2 nanocomposites were prepared by a modified onepot process. Then the europium coordination polymer was deposited on the surface of the Au NP@SiO2 by mixing 2,2＇-thiodiacetic acid [S（CH2 COO）2^（2-）, TDA] and Eu（NO3）3·6 H2 O in ethanol via a hydrothermal method. The maximum fluorescent enhancement factor of the nanocomposites was 6.81 at 30 nm thickness of silica between the core of the Au NP and the shell of TDA-Eu. The prepared nanocomposites exhibit more sensitive monitoring of reactive oxygen species.

Microbubble-enhanced ultrasound exposure improves gene transfer in vascular endothelial cells

AIM： To explore the effects of ultrasound exposure combined with microbubble contrast agent （SonoVue） on the permeability of the cellular membrane and on the expression of plasrnid DNA encoding enhanced green fluorescent protein （pEGFP） transfer into human umbilical vein endothelial cells （HUVECs）. METHODS： HUVECs with fluorescein isothiocyanatedextran （FD500） and HUVECs with pEGFP were exposed to continuous wave （1.9 MHz, 80.0 mW/cm^2） for 5 min, with or without a SonoVue. The percentage of FD500 taken by the HUVECs and the transient expression rate of pEGFP in the HUVECs were examined by fluorescence microscopy and flow cytornetry, respectively. RESULTS： The percentage of FDS00-positive HUVECs in the group of ultrasound exposure combined with SonoVue was significantly higher than that of the group of ultrasound exposure alone （24.0%± 5.5% vs 66.6% ± 4.1%, P 〈 0.001）. Compared with the group of ultrasound exposure alone, the transfection expression rate of pEGFP in HUVECs was markedly increased with the addition of SonoVue （16.1% ± 1.9% vs 1.5% ± 0.2%, P 〈 0.001）. No statistical significant difference was observed in the HUVECs survival rates between the ultrasound group with and without the addition of SonoVue （94.1% ± 2.3% vs 91.1% ± 4.1% ）. CONCLUSION： The cell membrane permeability of HUVECs and the transfection efficiency of pEGFP into HUVECs exposed to ultrasound are significantly increased after addition of an ultrasound contrast agent without obvious damage to the survival of HUVECs. This non- invasive gene transfer method may be a useful tool for clinical gene therapy of hepatic tumors.

Fluorescence Enhancement of Polyamine Derivatives of 1,8-Naphthalimide with Transition Metal Ions

A series of fluorescent chemosensors 1-3 were synthesized to detect transition metal ions. At the room temperature, fluorescence intensities of these chemosensors in acetonitrile without transition metal ions were found to be very weak, due to the process of the efficient intramolecular photoinduced electron transfer （PET）. However, after addition of the transition metal ions, the chemoscnsor 1-3 exhibits obvious fluorescence enhancement. Moreover, the intensity of the fluorescence emission of chemosensors increases significantly in the presence of Zn^2＋ and Cd^2＋. The fluorescent chemosensors with different polyamine as receptors show diverse affinity abilities to the transition metal ions and signal the receptor-metal ion interaction by the intensity change of fluorescence emission.

Fluorescence enhancement and cofluorescence in complexes of terbium(III) with trimellitic acid

The fluorescence of terbium （Ⅲ） was enhanced by about three orders of magnitude in the presence of trimellitic acid （benzene-1, 2, 4-tricarboxylic acid （TLA）） in aqueous solution at pH 6. The fluorescence intensity could be greatly increased when the system of Tb^3＋-TLA was treated with La^3＋ （or Gd^3＋） and TritonX- 100. The addition of La^3＋ （or Gd^3＋） enhanees the fluorescence of the system by about two orders of magnitude due to cofluorescenee, and the TritonX-100 micellar medium plays an important role for stabilization of the system. Both the intermolecular energy transfer mode and intramolecular energy transfer mode are responsible for the mechanism of fluorescence enhancement. In the optimum condi- tions, the fluorescence intensity is a linear function of Tb3~ concentration in the range of 7.8 × 10^-9-3.6 × 10^4 mol/L for the system Tb^3＋-La^3＋-TLA and 1.0 × 10^-8-4.7 × 10^-5 mol/L for the system Tb^3＋-Gd^3＋-TLA, and the limits of detection are 4.6 × 10^-10 mol/L and 6.0 × 10^-10 mol/L, respectively.

In vivo transfection of enhanced green fluorescent protein in rat retinal ganglion cells mediated by ultrasound-induced microbubbles

BACKGROUND： Studies have demonstrated that ultrasound-mediated microbubble destruction significantly improves transfection efficiency of enhanced green fluorescent protein （EGFP） in in vitro cultured retinal ganglial cells （RGCs）. OBJECTIVE： To investigate the feasibility of ultrasound-mediated microbubble destruction for EGFP transfection in rat RGCs, and to compare efficiency and cell damage with traditional transfection methods. DESIGN, TIME AND SETTING： In vivo, gene engineering experiment. The study was performed at the Central Laboratory, Institute of Ultrasonic Imaging, Chongqing Medical University from March to July 2008. MATERIALS： Eukaryotic expression vector plasmid EGFP and microbubbles were prepared by the Institute of Ultrasonic Imaging, Chongqing Medical University. The microbubbles were produced at a concentration of 8.7 × 10^11/L, with a 2-4 μm diameter, and 10-hour half-life in vitro. METHODS： A total of 50 Sprague Dawley rats were randomly assigned to four groups. Normal controls （n = 5） were infused with 5 μL normal saline to the vitreous cavity; the naked plasmid group （n = 15） was infused with 5 pL EGFP plasmid to the vitreous cavity; in the plasmid with ultrasound group （n = 15）, the eyes were irradiated with low-energy ultrasound wave （0.5 W/cm^2） for a total of 60 seconds （irradiated for 5 seconds, at 10-second intervals） immediately following infusion of EGFP plasmids to the vitreous cavities. In the microbubble-ultrasound group （n = 15）, the eyes were irradiated with the same power of ultrasonic wave immediately following infusion of microbubbles containing EGFP plasmids to the vitreous cavities. MAIN OUTCOME MEASURES： After 7 days, retinal preparations and EGFP expression in RGCs were observed by fluorescence microscopy. RGC quantification in the retinal ganglion cell layer was performed. In addition, EGFP mRNA expression was semi-quantitatively determined by RT-PCR. RESULTS： The transfection efficiency of EGFP to RGCs by microbubbles with ultrasound was significantly greater than the other groups, and no obvious damage was detected in the RGCs. CONCLUSION： Under irradiation of low-frequency ultrasound waves, ultrasound-mediated microbubble destruction was effective and resulted in safe transfection of the EGFP gene to the RGCs.

On the fluorescence enhancement mechanism of Er^(3+) in germanate glass containing silver particles

The spectral properties of trivalent erbium ions（Er^3＋） are systematically studied in a melt-quenched germanate glass（60 GeO2-20PbO-10BaO-10K2O-0.1Ag2O） containing silver（Ag） particles.Thermal treatment of the material leads to the precipitation of Ag particles as observed by transmission electron microscopy and confirmed by absorption spectrum for the obvious surface plasmon resonance peak of Ag particles.The fluorescence from Er^3＋ in the 10-min-annealed sample with Ag particles is found to be 4.2 times enhanced compared with the unannealed sample excited by 488-nm Ar＋ laser.A comparison is made between a spectral study performed on the unannealed Er^3＋-doped sample and the one annealed for 20 min.The data of absorption cross section and Judd-Ofelt intensity parameters show the agreement between the two samples no matter whether there are Ag particles,indicating that the introduction of Ag particles by post-heat treatment has no effect on the crystal field environment of Er^3＋ ions.The fluorescence enhancement is attributed to the surface plasmon oscillations of Ag particles in germanate glass.

Fluorescence and cofluorescence enhancement of Tb(Ⅲ) complexes with pyromellitic acid by M (M = Gd, La, Ca, and Sr ions)

Fluorescence and cofluorescence properties of Tb(Ⅲ) solid complexes werestudied using pyromellitic acid (PMA) as ligand and fluorescence inert ions as doping elements. Thecofluorescence enhancement, a result of ligand sensitized fluorescence, was observed in Tb(Ⅲ) solidcomplexes doped with fluorescent inert ions La(Ⅲ), Gd(Ⅲ), Ca(Ⅲ), and Sr(Ⅲ). The effect of thetype and content of doping elements on fluorescence enhancement was studied, and optimum conditionswere determined. The results show that Gd (La, Ca, Sr) has clear cofluorescence effect in solidcomplex Tb-M-PMA system, and in present work, rare earth complex fluorescent powder that emitsbright green fluorescence at ultraviolet excitation was obtained, which had potential application asfluorescent anti-counterfeit ink.

Peptide-RNA complexation-induced fluorescence“turn on”displacement assay for the recognition of small ligands targeting HIV-1 RNA

The regulator of expression of virion(Rev)protein binds specifically to the Rev-responsive element(RRE)RNA in order to regulate the expression of the human immunodeficiency virus(HIV)-1 genes.Fluorescence indicator displacement assays have been used to identify ligands that can inhibit the ReveRRE interaction;however,the small fluorescence indicators cannot fully replace the Rev peptide or protein.As a result,a single rhodamine B labeled Rev(RB-Rev)model peptide was utilized in this study to develop a direct and efficient ReveRRE inhibitor screening model.Due to photon-induced electron transfer quenching of the tryptophan residue on the RB fluorophore,the fluorescence of RB in Rev was weakened and could be dramatically reactivated by interaction with RRE RNA in ammonium acetate buffer(approximately six times).The interaction could reduce the electron transfer between tryptophan and RB,and RRE could also increase RB fluorescence.The inhibitor screening model was evaluated using three known positive ReveRRE inhibitors,namely,proflavin,6-chloro-9-[3-(2-chloroethylamino)propylamino]-2-methoxyacridine(ICR 191),and neomycin,as well as a negative drug,arginine.With the addition of the positive drugs,the fluorescence of the ReveRRE decreased,indicating the displacement of RB-Rev.This was confirmed using atomic force microscopy(AFM)and the fluorescence was essentially unaffected by the addition of arginine.The results demonstrated that RB-Rev can be used as a fluorescent probe for recognizing small ligands that target RRE RNA.The ReveRRE inhibitor screening model offers a novel approach to evaluating and identifying long-acting Rev inhibitors.

Fluorescence Enhancement of Metal-Capped Perovskite CH3NH3PbI3 Thin Films

We fabricate nano-structural metal films to improve photoluminescence of perovskite films. When the perovskite film is placed on an ammonia-treated alumina film, stronger photoluminescence is found due to local field en- hancement effects. In addition, the oxide spacer layer between the metal （e.g., AI, Ag and Au） substrate and the perovskite film plays an important role. The simulations and experiments imply that the enhancement is related to surface plasmons of nano-structural metals.

Fluorescence Emission Mediated by Metal-Dielectric-Metal Fishnet Metasurface: Spatially Selective Excitation and Double Enhancement

Enhancement of uorescent radiation is of great importance for applications including biological imaging,high-sensitivity detectors,and integrated light sources.Strong electromagnetic elds can be created around metallic nanoparticles or in gap of nanostructures,where the local state density of radiating mode is then dramatically enhanced.While enhanced uorescent emission has been demonstrated in many metallic nanoparticles and nanoparticle pairs,simultaneous mediation of absorption and emission processes of uorescent emitters remains challenging in metallic nanostructures.Here,we investigate uorescent emission mediated by metal-dielectric-metal fishnet metasurface,in which localized surface plasmon(LSP)and magnetic plasmon polaritons(MPPs)modes are coupled with absorption and emission processes,respectively.For absorption process,coupling of the LSP mode enables spatially-selective excitation of the uorescent emitters by rotating the polarization of the pump laser beam.In addition,the polarization-dependent MPP mode enables manipulation of both polarization and wavelength of the uorescent emission by introducing a rectangular fishnet structure.All the experimental observations are further corroborated by nite-difference time-domain simulations.The structure reported here has great potential for application to color light-emitting devices and nanoscale integrated light sources.